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It may not seem natural for a bird to fly under the sea. But since they abandoned the skies more than 50 million years ago, penguins have evolved some ingenious solutions to the challenges of a mostly marine life. Most importantly, perhaps, penguins have evolved an extraordinarily streamlined body that allows them to feed efficiently on the fish and other prey that live deep in the sea, far out of reach of their flying cousins. "Penguins have an almost perfectly hydrodynamic body profile -- just what you want if you live in a water world," says Gerald Kooyman, a University of California, San Diego biologist who has studied penguins for decades. In fact, Kooyman says, the penguin has among the most streamlined body shape ever gauged. A swimming Chinstrap penguin measuring more than seven inches wide, for instance, slices through the water with less resistance than a quarter-sized pebble.
Such streamlined design allows penguins to swim fast. While most cruise at about 5 miles per hour, some, such as Gentoo penguins, have been recorded blazing along at 15 miles per hour. Such bursts, often achieved by "porpoising," or repeatedly leaping out of the water, probably help penguins snag quick-moving prey and escape predators like leopard seals and killer whales. Sleek bodies also help penguins travel long distances. While most species appear to cover fewer than 60 miles in a single trip, some roam vast feeding territories. King and Emperor penguins, for instance, have been known to cover almost 1,000 miles on foraging trips that last up to a month, swimming more than 40 miles per day. Adelie penguins are believed to swim up to 3,000 miles to return to their spring nesting grounds, having spent the rest of the year roaming the drifting pack ice around Antarctica.
Penguins aren't just champion swimmers, however: Kooyman's research has helped reveal that they are also world-class divers. In the 1970s, in an effort to understand what Emperor penguins were doing at sea, Kooyman pioneered the use of automatic dive recorders -- devices attached to the penguins that recorded the depth and length of their dives. Though relatively crude, the first devices produced astonishing results: the penguins were revealed to be diving to depths of almost 900 feet in search of food. Later, more sophisticated devices recorded Emperors staying underwater for up to 11 minutes and diving to at least 1,766 feet. The devices showed that other penguins also ventured into deep waters far more often than biologists had thought possible. Researchers observed one Gentoo penguin, for instance, making more than 450 dives in 15 hours, some to lower than 300 feet.
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